Plant Uncoupling Mitochondrial Protein Activity in Mitochondria Isolated from Tomatoes at Different Stages of Ripening

In the present study we have observed a higher state of coupling in respiring mitochondriaisolated from green as compared to red tomatoes (Lycopersicon esculentum, Mill.). Greentomato mitochondria produced a membrane potential (ΔΨ) high enough to phosphorylate ADP,whereas in red tomato mitochondria, BSA and ATP were required to restore ΔΨ to the levelof that obtained with green tomato mitochondria. This supports the notion that such uncouplingin red tomato mitochondria is mediated by a plant uncoupling mitochondrial protein (PUMP;cf. Vercesi et al., 1995). Nevertheless, mitochondria from both green and red tomatoes exhibitedan ATP-sensitive linoleic acid (LA)-induced ΔΨ decrease providing evidence that PUMP isalso present in green tomatoes. Indeed, proteoliposomes containing reconstituted green or redtomato PUMP showed LA uniport and LA-induced H+ transport. It is suggested that the higherconcentration of free fatty acids (PUMP substrates) in red tomatoes could explain the lowercoupling state in mitochondria isolated from these fruits.